The molecular weight of polyacrylonitrile PAN can be controlled during its synthesis from acrylonitrile monomer through various methods and factors. The most common method for synthesizing PAN is free radical polymerization. Here are some factors that can be adjusted to control the molecular weight of PAN:1. Initiator concentration: The concentration of the initiator used in the polymerization process can significantly affect the molecular weight of the resulting polymer. A higher initiator concentration leads to a higher number of polymer chains being formed, resulting in lower molecular weight polymers. Conversely, a lower initiator concentration results in fewer polymer chains and higher molecular weight polymers.2. Reaction temperature: The temperature at which the polymerization reaction is carried out can also influence the molecular weight of PAN. Higher reaction temperatures can lead to faster decomposition of the initiator, resulting in a higher number of polymer chains and lower molecular weight polymers. Lower reaction temperatures can slow down the decomposition of the initiator, leading to fewer polymer chains and higher molecular weight polymers.3. Monomer concentration: The concentration of the acrylonitrile monomer in the reaction mixture can affect the molecular weight of the resulting PAN. Higher monomer concentrations can lead to higher molecular weight polymers, while lower monomer concentrations can result in lower molecular weight polymers.4. Reaction time: The duration of the polymerization reaction can also influence the molecular weight of PAN. Longer reaction times can lead to higher molecular weight polymers, while shorter reaction times can result in lower molecular weight polymers.5. Chain transfer agents: The use of chain transfer agents can help control the molecular weight of PAN by transferring the growing polymer chain to another molecule, effectively terminating the chain and starting a new one. By adjusting the concentration of the chain transfer agent, the molecular weight of the resulting polymer can be controlled.6. Polymerization method: The choice of polymerization method, such as bulk, solution, suspension, or emulsion polymerization, can also affect the molecular weight of PAN. Each method has its own set of conditions and parameters that can be adjusted to control the molecular weight of the resulting polymer.The properties of the resulting PAN polymer, such as its thermal stability, mechanical strength, and chemical resistance, are influenced by its molecular weight, degree of polymerization, and the presence of any impurities or additives. By controlling the molecular weight and other factors during the synthesis process, the desired properties of the PAN polymer can be achieved for specific applications.